The invention will be described in the field of the plasma display device. The transcoding method is used after a degamma function in a display receiver. FIG. 1 is a standard implementation circuit for encoding video data into subfield data. This circuit comprises a first memory 100 comprising 1024×12 bits for handling 10 bits video data YI[9:0]. A first look up table is stored in the memory 100 and used for remapping these data as described in EP patent application No. 1 353 314 for implementing the metacode concept or in EP patent application No 1 256 954 for implementing a Gravity Center Coding. At the output of the memory 100, 12 bits video signal YA[11:0] is obtained. The available 12-bits correspond to 8-bits integer resolution and 4-bits fractional resolution. Then, the 12-bits of video signal YA [11-0] are forwarded to a dithering circuit 110. In this circuit 110, the 4-bits of fractional resolution are added with the 4-bits of dithering and then truncated.
The video signal YB[7,0] from the circuit 110 is then forwarded to a second memory 120 comprising 256×16 bits. A second look-up table is stored in the memory 120 and is used for transforming the data YB[7:0] into subfield data SF[15:0].
Until now, a degamma function is implemented in the look-up table of the memory 100. Otherwise, in order not to lose significant bits, much more bits (typically 16 bits) would be required after the degamma function than the video input has. So, if the degamma function is made before the memory 100, this memory must have more inputs (16 bits), which will drastically increase the size of this memory. To go from 10 to 16 bits, the size of the memory is multiplied by 64.
And, on another hand, if a user wants to change the value of the degamma, to use a different degamma for each color or to use a specific degamma function, a specific look-up table should be generated for each case (if the degamma function can be known) and all of them should be stored.
For these reasons, it is necessary to separate the degamma function from the look-up table of the memory 100 and to create a transcoding circuit for transcoding 16 bits data (coming for example from a degamma block) into 10 bits data.
An object of the invention is to propose a method for transcoding a 16 bits word into a 10 bits word and, more generally, a method for transcoding a N bits word into a M bits word, N>M.